What is a good U-value for a wall in the UK?

A good wall U-value depends on the project type and the latest UK building regulations. New build walls often aim for lower U-values than extensions or upgrades. Always confirm the final target with current Part L guidance or building control.

Can I use this calculator for Recticel insulation?

Yes, this calculator can be used for indicative Recticel insulation estimates by entering the correct lambda value and insulation thickness. Always check the latest product datasheet before making a final decision.

Is this a formal U-value calculation?

No. This calculator provides an indicative estimate for planning and comparison. It is not a formal U-value certificate, SAP calculation, SBEM calculation or building control approval document.

What does W/m²K mean?

W/m²K means watts per square metre per degree Kelvin. It measures how much heat passes through a building element. A lower U-value usually means better thermal performance.

What is the difference between U-value and R-value?

U-value measures heat loss through a whole building element, so lower is better. R-value measures thermal resistance of a layer or material, so higher is better.

How do I calculate insulation thickness?

Insulation thickness is estimated by comparing the existing build-up, target U-value, insulation lambda value and required R-value. The calculator helps estimate how many millimetres of insulation may be needed.

Why does lambda value matter?

Lambda value shows how easily heat passes through a material. A lower lambda value usually means the insulation performs better, so less thickness may be needed to reach the same target.

Does meeting one U-value mean my whole building complies with Part L?

No. Meeting one element U-value does not guarantee whole-building compliance. Full compliance may also depend on thermal bridging, air tightness, ventilation, glazing, heating systems and other building design factors.

Do I need a condensation risk analysis?

You may need a condensation risk analysis when submitting formal plans, using complex build-ups or adding insulation where moisture could build up within the layers.

Can I use this calculator for flat roofs and pitched roofs?

Yes, the calculator can be used for indicative flat roof and pitched roof insulation estimates. For final specification, confirm the roof build-up, insulation position and current regulatory requirements.